“Senate Democrats have rightly reformed the filibuster, and the grass-roots base of the Democratic Party have their back for taking this important stand,” said Charles Chamberlain, executive director of the 1.2 million-strong Democracy for America. The group tends to favor challengers, but Chamberlain said the rules change would be a factor in endorsements and support.

“There's no question our members are extremely excited. They've been fighting for years,” Chamberlain said. His group, along with Credo Action and Daily Kos Action, delivered more than 285,000 petitions to Reid. Combined, he said, they represent 5 million members.

A coalition of groups including Democracy for America and CREDO Action had collected almost 300,000 signatures pushing Reid to act, but he gave them a victory before they even had the chance to deliver them.